FIG. 12 is a circuit block diagram of conventional backup power source device 5. Backup power source device 5 includes body case 1, capacitor 2, charging circuit 3, and output terminal 4. Capacitor 2 and charging circuit 3 are provided inside body case 1. Charging circuit 3 is provided in the charging path of capacitor 2. Output terminal 4 is provided in the output path of capacitor 2.
Power source (battery) 6 installed in an automobile cannot supply starting voltage to airbag starting circuit 7, in case where the battery is damaged by an accident, for example. In this case, backup power source device 5 supplies the starting voltage to airbag starting circuit 7 by discharging the electric charge accumulated in capacitor 2 thereof.
Airbag starting circuit 7 is started at the starting voltage supplied from backup power source device 5, and thereby airbag device 8 is operated. As a result, in case of an accident, backup power source device 5 can operate airbag device 8, thereby ensuring the safety of the passengers. For instance, Patent Literature 1 is known as information on the prior art documents related to this technique.